1. Field of the Invention
This invention relates to corrosion-inhibited antifreeze concentrate formulations, and to aqueous corrosion-inhibited antifreeze formulations for use in the cooling systems of internal combustion engines. More particularly, this invention relates to a corrosion-inhibited antifreeze concentrate formulation containing no phosphate, nitrite or amine compounds, and consisting essentially of a water soluble liquid alcohol freezing point depressant, a C.sub.6 -C.sub.12 aliphatic monobasic acid or alkali metal salt thereof, an alkali metal borate compound, and a hydrocarbyl triazole. The above described corrosion-inhibited antifreeze concentrate formulation and aqueous corrosion-inhibited antifreeze formulations derived via dilution of the concentrate with water provide unexpected synergistic corrosion protection for a variety of metals typically employed in engine cooling systems.
Automobile engine cooling systems contain a variety of metals, including copper, solder, brass, steel, cast iron, aluminum, magnesium, and their alloys. The possibility of corrosive attack on such metals is high, due to both the presence of various ions as well as the high temperatures, pressures, and flow rates found in such cooling systems. The presence of corrosion products within the cooling system can interfere with heat transfer from the engine combustion chambers, which may subsequently cause engine overheating and engine component failure due to excess metal temperatures. See generally Fay, R. H., "Antifreezes and Deicing Fluids," In: Kirk-Othmer Encyclopedia of Chemical Technology (1978 ed.) vol. 3, pp. 79-95. It would therefore be advantageous to develop corrosion-inhibited antifreeze formulations to avoid the abovedescribed problems.
A variety of corrosion inhibitors have previously been employed, both alone and in combination, to control the abovedescribed problems. However, many conventional corrosion inhibitors have themselves been found to cause problems when employed in antifreeze formulations. For example, phosphate compounds have been found to be good corrosion inhibitors for cast iron and steel, as well as for aluminum cavitation corrosion. Phosphates have also been employed to maintain the pH of antifreeze formulations.
Nevertheless, attendant problems may result from the use of phosphate compounds. For example, the dilution of an antifreeze formulation containing phosphate corrosion inhibitors with hard water will cause the precipitation of insoluble alkali earth phosphate salts from the aqueous antifreeze solution. This precipitation causes rapid depletion of phosphate in solution, and in turn causes a decrease in corrosion protection within the antifreeze formulation. In addition, the precipitating solids will scale and eventually plug the passages of the engine cooling system, which is detrimental to heat transfer from the engine combustion chambers. The use of phosphate-containing antifreeze formulations is thus precluded in many areas, where only hard water (i.e. water of greater than 150 ppm as CaCO.sub.3 total hardness) is available to dilute the antifreeze concentrate. In fact, several European automakers have banned the use of phosphate-containing antifreeze formulations in their automobiles due to the abovedescribed hard water compatibility problems. To circumvent this problem, the use of various anti-precipitation additives in phosphate-containing antifreeze formulations has been proposed, see co-assigned U.S. patent application Ser. No. 834,678 (Triebel et al.), filed on Nov. 28, 1986 (D#80,528). However, the use of such additives increases the overall cost of the formulation.
Other conventional corrosion inhibitors also have problems associated with their use in antifreeze formulations. Amine and nitrite compounds, which are often employed as corrosion inhibitors in antifreeze formulations may form dangerous nitroso compounds when used together. It would therefore be advantageous to develop an antifreeze formulation which provides adequate protection of a variety of metals without employing phosphate, amine, or nitrite compounds.
It is the object of the instant invention to provide a corrosion-inhibited antifreeze concentrate formulation and an aqueous corrosion-inhibited antifreeze formulation containing no phosphate, nitrite, or amine compounds, yet remaining effective in preventing corrosion in a variety of metals. The instant invention provides synergistic corrosion protection for various metals beyond what would ordinarily be expected from the combination of the individual corrosion-inhibiting components of the invention.
2. Information Disclosure Statement
It is well known that various monobasic and dibasic acids are effective as corrosion inhibitors, either alone or in combination with other corrosion inhibitors. For example, the use of sodium salts of various monobasic and dibasic acids as mild steel corrosion inhibitors is disclosed in Hersch, P., et al., "An Experimental Survey of Rust Preventives in Water --II. The Screening of Organic Inhibitors," Journal of Applied Chemistry, Vol. 11 (July, 1961), pp. 254-55. Many U.S. and foreign patent references also disclose the use of various monobasic or dibasic acids or salts as corrosion inhibitors. For example:
Co-assigned U.S. patent application Ser. No. 880,473, (Van Neste et al.) filed on June 30, 1986 (D#71,000-TF-150) discloses a corrosion-inhibited antifreeze composition comprising a water soluble liquid alcohol freezing point depressant, an alkyl benzoic acid or salt thereof, a C.sub.8 -C.sub.12 aliphatic monobasic acid or salt thereof, and a hydrocarbyl triazole;
Co-assigned U.S. patent application Ser. No. 819,321 (Trievel et al.), filed on Jan. 16,1986 (D#80,502) discloses a stabilized corrosion-inhibited antifreeze formulation which comprises at least one C.sub.5 -C.sub.16 monobasic or dibasic acid/salt and a precipitation-inhibiting hydrocarbyl aminophosphonic acid/salt or polyacrylic acid/polyacrylate stabilizer;
Co-assigned U.S. Pat. No. 4,657,689 (Darden) discloses a corrosion-inhibited antifreeze composition comprising a C.sub.5 -C.sub.16 aliphatic monobasic acid/salt, a -C.sub.5 C.sub.16 hydrocarbyl dibasic acid/salt, a hydrocarbyl azole, and a hydrocarbyl C.sub.10 -C.sub.20 alkali metal sulfonate;
Co-assigned U.S. Pat. No. 4,647,392 (Darden et al.) discloses a corrosion-inhibited antifreeze formulation comprising the combination of a C.sub.5 -C.sub.16 aliphatic monobasic acid/salt, a C.sub.5 -C.sub.16 hydrocarbyl dibasic acid/salt, and a hydrocarbyl triazole;
Co-assigned U.S. Pat. No. 4,588,513 (Triebel et al.) discloses a non-borate and non-phosphate corrosion inhibited antifreeze formulation comprising a dibasic acid or salt, an alkali metal silicate, and a triazole;
Co-assigned U.S. Pat. No. 4,578,205 (Yeakey et al.) discloses a corrosion inhibitor for use in antifreeze formulations which is a combination of the dibasic acid methylene azelaic acid and optional conventional corrosion inhibitors, including alkali metal borates;
Co-assigned U.S. Pat. No. 4,561,990 (Darden) discloses a corrosion inhibitor useful in preventing the corrosion of high lead solders in phosphate-based antifreeze formulations, the inhibitor comprising a C.sub.8 -C.sub.12 dicarboxylic acid or salt, an alkali metal molybdate, and optionally containing a conventional corrosion inhibitor such as an alkali metal borate;
U.S. Pat. No. 4,450,088 (Wilson et al.) discloses a corrosion inhibited antifreeze formulation comprising the mixture of an amino acid or derivative thereof, an alkali metal phosphate, a heterocyclic nitrogen compound, and a conventional corrosion inhibitor which may be borax;
U.S. Pat. No. 4,382,008 (Boreland et al.) discloses a corrosion inhibitor for aqueous media comprising a triazole, a benzoate, a silicate, the alkali metal salt of a C.sub.7 -C.sub.13 dibasic acid, and an alkali metal borate;
U.S. Pat. No. 4,342,596 (Conner) discloses an aqueous corrosion inhibitor which is a mixture of a C.sub.8 -C.sub.20 aliphatic monobasic acid, a lubricant, an amino alkylalkanolamine, an aromatic mono- or polycarboxylic acid, and an amine which forms a water soluble salt with the aromatic acid;
U.S. Pat. No. 3,962,109 (Oberhofer et al.) discloses a cleaner-inhibitor composition for use in automobile cooling systems, the composition comprising an amino polycarboxylic acid, an alpha-hydroxy carboxylic acid, an azole compound, an alkali metal borate, an alkali metal nitrite, and an alkali metal silicate; and
U.S. Pat. No. 2,832,742 (Weltman) discloses a water soluble corrosion inhibitor which is a mixture of C.sub.7 -C.sub.18 high molecular weight aliphatic carboxylic acids and p-tert butyl benzoic acid;
Many of the abovedescribed references employ borax or alkali metal borate compounds as optional corrosion inhibitors in addition to a monobasic or dibasic acid or salt corrosion inhibitor. However, the instant invention is distinguishable from other compositions employing monobasic or dibasic acids or salts in combination with borax or alkali metal borate compounds in that the instant invention offers synergistic corrosion protection for a variety of metals that is unexpected based upon the individual corrosion-inhibiting performance of monobasic or dibasic acids or salts and borax or alkali metal borate compounds alone.